1. Field of the Invention
The present invention relates generally to solar cells, and more particularly but not exclusively to solar cell fabrication tools and processes.
2. Description of the Background Art
Solar cells are well known devices for converting solar radiation to electrical energy. They may be fabricated on a solar cell substrate, such as a semiconductor wafer, using semiconductor processing technology. A solar cell includes P-type and N-type diffusion regions that form a junction. Solar radiation impinging on the solar cell creates electrons and holes that migrate to the diffusion regions, thereby creating voltage differentials between the diffusion regions. In a backside contact solar cell, both the diffusion regions and the metal contacts coupled to them are on the backside of the solar cell. The metal contacts allow an external electrical circuit to be coupled to and be powered by the solar cell.
An edge of a solar cell substrate may be coated with a dielectric for electrical isolation and to prevent metal deposition or growth on the substrate perimeter. The conventional approach for applying the coating material is to contact the edge of the substrate with a roller. The roller has a groove with a surface that is pushed against the edge of the substrate. Coating material supplied to the groove gets applied to the edge of the substrate when the roller and the substrate are rotated. The coating material may comprise thermal ink that needs to be cured in a large drying oven in a separate process step. The use of thermal ink thus necessitates relatively large capital investment due to the cost and large footprint of associated ovens. In addition when using a thermal oven, the materials deposited on the wafer surface in previous processing steps could be affected by exposure to oven temperature. Other problems associated with previous approaches to edge coating include stress applied to the substrate by direct mechanical contact with the applicator and poor reliability of the edge coat in processes using thermal ink.